Sensor and control system for an automotive air conditioning system

ABSTRACT

An air conditioning system including a refrigerant circulation route, a compressor, a condenser, an expansion valve, an evaporator and a pressure sensor for detecting pressure in the circulation route comprises a refrigerant phase detecter provided on the circulation route between the condenser and the evaporator where the refrigerant should be in a liquid phase for detecting whether the refrigerant is in a liquid phase or in a vapor phase and a control for determining whether the compressor is in a locked state in accordance with the signals from the refrigerant phase detecter and the pressure sensor. The air conditioning system can precisely determine and detect both compressor lock up and refrigerant leakage without providing a rotation detecting sensor for the compressor.

This application is a division of application Ser. No. 07/789,991, filedNov. 12, 1991 now U.S. Pat. No. 5,197,298.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an air conditioning system, and moreparticularly to an air conditioning system suitable for use in vehicles.

2. Description of the Prior Art

A typical conventional air conditioning system, for example, a typicalconventional air conditioning system for vehicles is constituted, forexample, as shown in FIG. 8. A refrigerant such as freon gas iscirculated in circulation route 1 formed from pipe 2. Compressor 3,condenser 4, expansion valve 11 and evaporator 5 are provided incirculation route 1 in this order in the circulation direction of therefrigerant which is shown by arrow "A". The endothermic surface ofevaporator 5 is exposed to the interior of the vehicle (not shown).After the refrigerant is compressed by compressor 3, the refrigerant istransformed in phase from a high-pressure gas to a high-pressure liquidin condenser 4 and further to a low-pressure gas as it passes throughexpansion valve 11 and evaporator 5. When the refrigerant is transformedfrom liquid phase to gaseous phase (vapor phase) by evaporator 5, therefrigerant absorbs heat from the interior of the vehicle and thevehicle interior is cooled. Expansion valve 11 is provided betweencondenser 4 and evaporator 5. Expansion valve 11 reduces the pressure ofthe refrigerant to a relatively low pressure so that the liquefiedhigh-pressure refrigerant can be easily vaporized when it passes throughevaporator 5.

Compressor 3 is driven by engine 6 of the vehicle via pulley 6A, V belt8 and pulley 7A attached to electromagnetic clutch 7. Electromagneticclutch 7 controls the drive of compressor 3. Electromagnetic clutch 7 isinitially controlled by an air conditioner switch (not shown). When theair conditioner switch is turned "on", electromagnetic clutch 7 isactuated and compressor 3 is driven by engine 6.

A receiver tank 9 is provided in circulation route 1 at a positionbetween condenser 4 and evaporator 5. Receiver tank 9 temporarily storesthe refrigerant which has been in a liquid phase. On top of receivertank 9, an inspection hole 9A is provided for observing the liquefactionof the refrigerant. Pressure sensor 10 is attached to receiver tank 9.Pressure sensor 10 detects the pressure of the refrigerant in receivertank 9. When the pressure in receiver tank 9 exceeds a predeterminedpressure, a signal is sent to a control unit (not shown). The controlunit sends an "off" signal to clutch 7 when pressure sensor 10 detectsan excessive pressure, and the clutch is released and compressor 3 isstopped. The bursting of pipe 2 or other components can thus beprevented by stopping compressor 3. When the pressure of the refrigerantreduces to another predetermined pressure from the excessive pressure,pressure sensor 10 sends a signal to the control unit. The control unitsends an "on" signal to clutch 7, and compressor 3 is driven again. Thison-off operation of compressor 3 in accordance with the detection of thepressure of the refrigerant by pressure sensor 10 is automaticallycontrolled. Damage to pipe 2 or other components and the overheating ofcompressor 3 can be prevented by this control.

In such a conventional air conditioning system, there are the followingproblems. For example, in a case where foreign materials intervenebetween the cylinder and the piston of compressor 3, the compressor maybe locked In such a case, the refrigerant cannot circulate incirculation route 1, and the cooling ability of the system quicklydecreases. The driver of the vehicle cannot determine whether thereduction of the cooling ability is caused by the lock up of compressor3 or by the leakage of the refrigerant. Therefore, in the conventionalair conditioning system, a rotation detecting sensor is attached to theoutside of compressor 3, and the lock of the compressor is detected bythe sensor.

In such a conventional air conditioning system, however, since the sizeand type of compressor 3 vary depending upon the type of vehicle, it isoften necessary to reconstruct the compressor in order to attach therotation detecting sensor to the outside of the compressor. The workingor processing of the reconstruction of the compressor is very timeconsuming and costly.

Moreover, even if the rotation detecting sensor is attached to thecompressor, refrigerant leakage cannot be detected.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide an airconditioning system which can determine and detect both of the lock of acompressor and the leakage of refrigerant without providing a rotationdetecting sensor for the compressor.

To achieve this object, an air conditioning system according to thepresent invention is herein provided. The air conditioning systemincludes a circulation route for circulating a refrigerant, acompressor, a condenser, an expansion valve and an evaporator disposedon the circulation route in this order in the circulation direction ofthe refrigerant, and a pressure sensor for detecting a pressure in thecirculation route. The air conditioning system comprises a refrigerantphase detecting means provided on a path of the circulation routebetween the condenser and the evaporator where the refrigerant should bein a liquid phase for detecting whether the refrigerant is in a liquidphase or in a vapor phase, and means for determining whether thecompressor is in a locked state in accordance with the signals from therefrigerant phase detecting means and the pressure sensor.

In the air conditioning system, the refrigerant phase detecting meansdetects whether there exists some refrigerant of vapor phase in therefrigerant which should be in liquid phase in the path between thecondenser and the evaporator. In addition, the determining meansdetermines whether there are refrigerant leaks and whether thecompressor is in a locked state in accordance with the signals from therefrigerant phase detecting means and the pressure sensor. Therefore,both refrigerant leakage and the compressor lock up are determinedwithout using a rotation detecting sensor for the compressor. By thisdetermination, damage to pipes and other components and compressoroverheating can be prevented, thus minimizing the amount of repair worknecessary. As a result, the reliability and the life of the system canbe greatly increased.

BRIEF DESCRIPTION OF THE DRAWINGS

Some preferred exemplary embodiments of the invention will now bedescribed with reference to the accompanying drawings, which are givenby way of example only, and are not intended to limit the presentinvention.

FIG. 1 is a schematic view of an air conditioning system according to afirst embodiment of the present invention.

FIG. 2 is an enlarged sectional view of a flow sensor of the airconditioning system shown in FIG. 1.

FIG. 3 is a block diagram showing the control system of the airconditioning system shown in FIG. 1.

FIG. 4A is a graph showing the characteristic of the output signal ofthe flow sensor when a refrigerant leak is present in the airconditioning system shown in FIG. 1.

FIG. 4B is a graph showing the characteristic of the output signal ofthe flow sensor when a compressor is locked in the air conditioningsystem shown in FIG. 1.

FIG. 5A is a graph showing the characteristic of the output signal of apressure sensor when a refrigerant leak is present in the airconditioning system shown in FIG. 1.

FIG. 5B is a graph showing the characteristic of the output signal of apressure sensor when a compressor is locked in the air conditioningsystem shown in FIG. 1.

FIG. 6 is a flowchart showing the control in the air conditioning systemshown in FIG. 1.

FIG. 7 is a vertical sectional view of a flow sensor of an airconditioning system according to a second embodiment of the presentinvention.

FIG. 8 is a schematic view of a prior art air conditioning system.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Referring to the drawings, FIGS. 1-6 illustrate an air conditioningsystem according to a first embodiment of the present invention. In FIG.1, a refrigerant such as freon gas is circulated in a circulation route21 formed from a pipe 22. Compressor 23, condenser 24, expansion valve31 and evaporator 25 are provided on circulation route 21 in this orderin the circulation direction of the refrigerant which is shown by arrow"A". The endothermic surface of evaporator 25 is exposed to the interiorof the vehicle (not shown). After the refrigerant is compressed bycompressor 23, the refrigerant is transformed in phase from ahigh-pressure gas to a high-pressure liquid in condenser 24 and furtherto a low-pressure gas in expansion valve 31 and evaporator 25. When therefrigerant is transformed from liquid phase to gaseous phase (vaporphase) by evaporator 25, the refrigerant absorbs heat from the interiorof the vehicle and the interior of the vehicle is cooled. Expansionvalve 31 is provided between condenser 24 and evaporator 25. Expansionvalve 31 reduces the pressure of the refrigerant to a relatively lowpressure in order to facilitate vaporization of the liquefiedhigh-pressure refrigerant when it passes through evaporator 25.

Compressor 23 is driven by an engine 26 of the vehicle via pulley 26A, Vbelt 28 and pulley 27A attached to electromagnetic clutch 27.Electromagnetic clutch 27 controls the drive of compressor 23 bycontrolling the transmission of the driving force of the engine to thecompressor. Electromagnetic clutch 7 is initially controlled by an airconditioner switch 48 (FIG. 3). When the air conditioner switch isturned "on", electromagnetic clutch 27 is actuated and compressor 23 isdriven by engine 26.

A receiver tank 29 is provided on circulation route 21 at a positionbetween condenser 24 and evaporator 25. Receiver tank 29 temporarilystores the refrigerant which has been in a liquid phase. On top ofreceiver tank 29, an inspection hole 29A is provided for observing theliquefaction of the refrigerant. Pressure sensor 30 is attached toreceiver tank 29. Pressure sensor 30 detects refrigerant pressure inreceiver tank 29, and the detected signal is sent to a control unit 44(FIG. 3).

Flow sensor 41 is provided as a refrigerant phase detecting means on apath of circulation route 21 between condenser 24 and evaporator 25where the refrigerant should be in a liquid phase, which, in thisembodiment, is at a position downstream of receiver tank 29. Casing 42of flow sensor 41 has a cylindrical portion 42A and a refrigerantstagnation portion 42B formed to project downward, as shown in FIG. 2.The ends of the cylindrical portion 42A are connected to pipe 22, andthe portion forms a part of circulation route 21. The refrigerantstagnation portion 42B provides a section of stagnant flow in therefrigerant flowing the portion 42A in the direction shown by arrows"A". Stagnation portion 42B temporarily stores refrigerant therein.

Thermistor 43, a self-exothermic type temperature detecting thermistor,is provided in refrigerant stagnation portion 42B at a position near thebottom. Thermistor 43 is heated to a predetermined temperature by thecurrent supplied from a battery provided as a power source (not shown).The heated thermistor 43 is cooled by the refrigerant in stagnationportion 42B. The degree of the cooling of the heated thermistor 43changes depending on the phase state of the refrigerant, namely, onwhether the refrigerant is in a liquid phase or a vapor phase. Thevariation in the temperature due to the self-exothermic operation ofthermistor 43 is detected as the variation of a voltage signal "V_(F) ".Although self-exothermic type thermistor 43 is used in this embodiment,another element, for example, a self-exothermic type Posistor (a kind ofa self-exothermic type thermistor) may be used.

FIG. 3 illustrates the control system of the air conditioning system.Control unit 44 is constructed from a microcomputer, and comprisesinput-output unit 45, processor 46 and memory 47, as shown in FIG. 3.Air conditioner switch 48, pressure sensor 30 and flow sensor 41 areconnected to the input side of input-output unit 45, and clutch 27,compressor lock warning device 49 and refrigerant leak warning device 50are connected to the output side of the input-output unit. These warningdevices 49 and 50 are constructed from, for example, a lamp, a buzzer ora speech synthesis device provided on the dash board of the vehicle (notshown). Memory 47 includes ROMs (read only memory) and RAMs (randomaccess memory) and has a memory area 47A. A predetermined value(voltage) "V_(F0) " to be compared with the signal "V_(F) " from flowsensor 41 and a predetermined value (voltage) "V_(P0) " to be comparedwith the signal "V_(P) " from pressure sensor 30 are stored in memoryarea 47A. A program such as shown in FIG. 6, is stored in memory 47 anddetermines whether the refrigerant is in a liquid phase or in a vaporphase and whether compressor 23 is locked by comparing the signals fromflow sensor 41 and pressure sensor 30 with the above predeterminedvalues.

FIGS. 4A and 4B show the characteristics of the output voltages(resistance values) Of thermistor 43 which functions as the sensingportion of flow sensor 41. When refrigerant leaks, the output voltage"V_(F) " changes as shown in FIG. 4A. When compressor 23 is locked, theoutput voltage "V_(F) " changes as shown in FIG. 4B. FIGS. 5A and 5Bshow the characteristics of the output voltages of pressure sensor 30.When the refrigerant leaks, the output voltage "V_(P) " changes as shownin FIG. 5A. When compressor 23 is locked, the output voltage "V_(P) "changes as shown in FIG. 5B. According to these characteristics,variations of the output voltage "V_(F) " of flow sensor 41 and theoutput voltage "V_(P) " of pressure sensor 30 differ from each otherwhen the refrigerant leaks and when compressor 23 is locked.Particularly, when compressor 23 is locked, because the operation of thecompressor is stopped, the output voltage "V_(F) " of flow sensor 41 andthe output voltage "V_(P) " of pressure sensor 30 rapidly change asshown in FIGS. 4B and 5B. When the refrigerant leaks, however from thesystem, because the refrigerant gradually leaks in spite of thecontinuous operation of compressor 23, the output voltage "V_(P) " ofpressure sensor 30 gradually changes as shown in FIG. 5A.

In the above system, when air conditioner switch 48 is turned "on",clutch 27 is closed, the driving force of engine 26 is transmitted tocompressor 23 via the clutch, and the compressor is driven. At the sametime when the air conditioning system is started, the control shown inFIG. 6 is also started.

In FIG. 6, after the control is started, the output voltage "V_(F) " offlow sensor 41 and the output voltage "V_(P) " of pressure sensor 30 areread at step S1. At step S2, it is determined whether the output voltage"V_(F) " of flow sensor 41 is greater than the predetermined voltage"V_(F0) " which has been stored in memory area 47A of memory 47 and atthe condition of which the refrigerant transforms from liquid phase tovapor phase. If the output voltage "V_(F) " is determined to be greaterthan the voltage "V_(F0) ", the refrigerant which should be in a liquidphase is determined to be in a vapor phase, and the flow proceeds tostep S3. If the output voltage "V_(F) " is determined not to be greaterthan the voltage "V_(F0) ", the refrigerant is determined to be in aliquid phase, and the flow returns to step S1. In this condition, theoperation of compressor 23 is continued.

At step S3, it is determined whether the voltage "V_(P) " pressuresensor 30 read at step S1 is greater than the predetermined voltage"V_(P0) " which has been stored in memory area 47A of memory 47. If theoutput voltage "V_(P) ", it is determined to be greater than the voltage"V_(P0) ", it is determined that compressor 23 is not locked, and theflow proceeds to step S4. If the output voltage "V_(P) " is determinednot to be greater than the voltage "V_(P0) ", the flow proceeds to stepS6.

At step S4, since the output voltage "V_(F) " of flow sensor 41 isdetermined to be greater than the predetermined voltage "V_(F0) " atstep S2 and the output voltage "V_(P) " of pressure sensor 30 isdetermined to be greater than the predetermined voltage "V_(P0) " atstep S3, it can be determined that there is a refrigerant leak, and awarning signal is issued. The warning is given to the driver of thevehicle by warning device 50. Then, the flow proceeds to step S5. Atstep S5, clutch 27 is released, compressor 23 and engine 26 aredisconnected and the operation of the compressor is stopped.

At step S6, since the output voltage "V_(F) " of flow sensor 41 isdetermined to be greater than the predetermined voltage "V_(F0) " atstep S2 and the output voltage "V_(P) " of pressure sensor 30 isdetermined not to be greater than the predetermined voltage "V_(P0) " atstep S3, it can be determined that compressor 23 is in a locked state,and a warning signal is issued. The warning is given to the driver ofthe vehicle by warning device 49. Then, the flow proceeds to step S5. Asdescribed above, the operation of compressor 23 is stopped by therelease of clutch 27 at step S5.

In the above flow, step $2 and step S3 constitute means for determiningwhether compressor 23 is in a locked state in accordance with thesignals from the refrigerant phase detecting means (flow sensor 41) andpressure sensor 30.

Thus, in this system, whether there exists a refrigerant of a vaporphase in the refrigerant which should be in a liquid phase is determinedby the signal from flow sensor 41 as well as whether compressor 23 is ina locked state or whether there is a refrigerant leak is determined bythe variation of the pressure of the refrigerant detected by pressuresensor 30. Compressor lock warning device 49 and refrigerant leakwarning device 50 can properly operate, and the driver can know theprecise reason why the cooling ability reduces. Since the servicetechnician can quickly and precisely recognize the reason from thewarnings, the air conditioning system can be quickly and easilyrepaired. Moreover, since compressor 23 is immediately stopped when anyof warning signals is issued, further damage such as compressor seizure,can be prevented. As a result, the life of compressor 23 is effectivelyextended and the reliability of the air conditioning system is greatlyincreased. Furthermore, since it is not necessary to provide a rotationdetecting sensor to the outside of the compressor, the present systemcan be easily installed or retrofitted to any type of compressors orvehicles.

Although self-exothermic type thermistor 43 is provided in refrigerantstagnation portion 42B, other structures can be employed. For example,FIG. 7 illustrates the attachment structure of a flow sensor 51according to a second embodiment of the present invention. Flow sensor51 is constructed as a plug type sensor, and attached directly to thewall of pipe 22 forming refrigerant circulation route 21. Aself-exothermic type thermistor 52 is installed in sensor 51. This flowsensor 51 may be attached to receiver tank 29.

The type of the flow sensor also is not particularly restricted. Forexample, a capacitance type flow sensor or a resistance type flow sensormay be employed.

Although several preferred embodiments of the present invention havebeen described herein in detail, it will be appreciated by those skilledin the art that various modifications and alterations can be made tothese embodiments without materially departing from the novel teachingsand advantages of this invention. Accordingly, it is to be understoodthat all such modifications and alterations are included within thescope of the invention as defined by the following claims.

What is claimed is:
 1. A system for discriminating between types ofmalfunctions within a refrigerant circuit in an air conditioning systemcomprising:container means, coupled to said refrigerant circuit, forreceiving at least a portion of a refrigerant from said refrigerantcircuit, flow stagnating means, coupled to said container means, forproviding a portion of said container means with a stagnant flow of therefrigerant, temperature sensing means, coupled to said container means,for sensing a temperature of the stagnant flow of refrigerant andoutputting a temperature signal, first comparator means, coupled to saidtemperature sensing means, for comparing the temperature signal with afirst predetermined value, pressure sensing means, coupled to saidrefrigerant circuit, for detecting a pressure in said refrigerantcircuit and outputting a pressure signal, second comparator means,coupled to said pressure sensing means, for comparing the pressuresignal with a second predetermined value, wherein one type ofmalfunction exists if the temperature signal exceeds the firstpredetermined value and the pressure signal is less than the secondpredetermined value, and another type of malfunction exists if thetemperature signal exceeds the first predetermined value and thepressure signal exceeds the second predetermined value.